|Publication number||US7391791 B2|
|Application number||US 10/322,335|
|Publication date||Jun 24, 2008|
|Filing date||Dec 17, 2002|
|Priority date||Dec 17, 2001|
|Also published as||US8406257, US8942252, US20030221161, US20080240165, US20100153512, US20130290461, WO2003054686A2, WO2003054686A3|
|Publication number||10322335, 322335, US 7391791 B2, US 7391791B2, US-B2-7391791, US7391791 B2, US7391791B2|
|Inventors||Edward Balassanian, Scott W. Bradley|
|Original Assignee||Implicit Networks, Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (13), Referenced by (21), Classifications (13), Legal Events (9)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application claims the benefit of U.S. Provisional Application No. 60/341,574 filed Dec. 17, 2001, which is incorporated herein by reference in its entirety.
The described technology relates to rendering of content at multiple rendering devices in a synchronized manner.
Multimedia presentations that are presented on different rendering devices (e.g., video display and stereo system) typically require that the different content of the presentation be rendered in a synchronized manner. For example, a multimedia presentation may include video, audio, and text content that should be rendered in a synchronized manner. The audio and text content may correspond to the dialogue of the video. Thus, the audio and text contents need to be rendered in a synchronized manner with the video content. Typically, the content of a multimedia presentation is stored at a single location, such as on a disk drive of a source device. To render the presentation, the source device retrieves each different type of content and sends it to the appropriate rendering device to effect the multimedia presentation. The source device then sends the content to the rendering devices in sufficient time so that the rendering devices can receive and render the content in a timely manner.
Various rendering devices, however, may have different time domains that make the rendering of the multimedia presentation in a synchronized manner difficult. For example, video and audio rendering devices may have system clocks that operate at slightly different frequencies. As a result, the video and audio content will gradually appear to the person viewing the presentation to be out of synchronization. The rendering of content in a synchronized manner is made even more difficult because some rendering devices may have multiple time domains. For example, an audio rendering device may have a system clock and a clock on a digital signal processing (“DSP”) interface card. In such a case, the combination of clocks may result in the presentation becoming even more quickly out of synchronization.
It would be desirable to have the technique that would facilitate the rendering of the multimedia presentation in a synchronized manner.
A method and system for synchronizing the rendering of content at various rendering devices is provided. In one embodiment, each rendering device has a device time and a rendering time. The device time is the time as indicated by a designated clock (e.g., system clock) of the rendering device. The rendering time is the time represented by the amount of content that has been rendered by that rendering device. For example, if a rendering device is displaying 30 frames of video per second, then the rendering time will be 15 seconds after 450 frames are displayed. The rendering time of content at a rendering device has a “corresponding” device time, which is the device time at which the rendering time occurred. For example, the rendering time of 15 seconds may have a corresponding device time of 30 minutes and 15 seconds when the rendering device initialized 30 minutes before the start of rendering the video. To help ensure synchronization of rendering devices, the synchronization system designates one of the rendering devices as a master rendering device and designates all other rendering devices as slave rendering devices. Each slave rendering device adjusts the rendering of its content to keep it in synchronization with the rendering of the content at the master rendering device. The master rendering device sends a message with its rendering time and corresponding device time to the slave rendering devices. Each slave rendering device, upon receiving the message from the master rendering device, determines whether it is synchronized with the master rendering time. If not, the slave rendering device adjusts the rendering of its content to compensate for the difference between the master rendering time and the slave rendering time. A slave rendering device can determine the amount it is out of synchronization by comparing its slave rendering time at a certain slave device time to the master rendering time at that same device time. Alternatively, the amount can be determined by comparing its slave device time at a certain rendering time to the master device time at that same rendering time. In another embodiment, the synchronization system can define a default rendering time for the synchronization. In such a case, the master rendering device need only include its effective device time that corresponds to the default rendering time in the message that is sent to the slave rendering devices. For example, the default rendering time might be the rendering time of zero. In such a case, the master rendering device can subtract its current rendering time from its current device time to give its effective device time at rendering time zero. A slave rendering device, knowing the default rendering time, can determine whether it is synchronized and the variation in rendering time between the master rendering device and the slave rendering device.
In one embodiment, the synchronization system allows for two sources of content to be synchronized even though the rendering times of the sources are not themselves synchronized. For example, two separate sources may be video transmitted via satellite and audio transmitted via land telephone lines. If audio is being transmitted and then a few seconds later the corresponding video starts to be transmitted, then the rendering times of zero for the audio and video will not correspond to a synchronized state. For example, the video at the video rendering time of zero should be rendered at the same time as the audio with the audio rendering time of five is rendered. This difference in rendering times is referred to as source offset. In addition, the difference in the propagation delay resulting from the different transmission paths of the video and audio may be variable and thus contribute to a variation in synchronization that is variable and is not known in advance.
To account for this lack of synchronization, the synchronization system allows a user (e.g., the person viewing the content) to manually account for the variation. For example, if the video and audio are rendered via a personal computer, the synchronization system may display a dial or a slider on a user interface that the user can adjust to indicate the difference in the rendering times. If the video is rendered five seconds after the corresponding audio, then the user can indicate via the user interface that the offset is five seconds. In such a case, the synchronization system may use the offset to adjust the rendering time of the audio so that the audio associated with the adjusted audio rendering time should be rendered at the same time as the video content with the same video rendering time. The synchronization system could buffer the audio to account for the offset.
The synchronization system in one embodiment factors in the differences in the time domains of the various rendering devices when evaluating synchronization. The rendering devices exchange device time information so that the rendering devices can account for the differences in the time domains of the other rendering devices. Each rendering device may send to the other rendering devices a time domain message that includes its current device time (i.e., send time) along with the time it received the last time domain message (i.e., receive time) from each of the other rendering devices and the send time of that last time domain message. When a rendering device receives such a time domain message, it calculates the time differential between its time domain and the time domain of the sending rendering device. In one embodiment, the synchronization system calculates the time domain differential by combining the difference in send and receive times for the last messages sent to and received from another device in a way that helps factor out the transmission time of the messages. A slave rendering device can then use this time domain differential to convert the master device time to the time domain of the slave when synchronizing the rendering of content. In one embodiment, each rendering device broadcasts at various times its time domain message. The time domain message includes a received time for a message received for each of the other rendering devices. Each rendering device receives the broadcast time domain message. The receiving rendering device can then calculate its time domain differential with the broadcasting rendering device. In this way, time domain differentials can be determined on a peer-to-peer basis without the need for a master device to keep a master time and by broadcasting the time domain messages, rather then sending separate time domain messages for each pair of devices.
where Diff is the time domain differential, RT is receive time, and ST is send time. Device 1 then sends a time domain message 203 to device 2 that includes its device time, referred to as “sendtime3” along with sendtime2 and receivetime2. When device 2 receives the time domain message, it stores sendtime2, receivetime2, and sendtime3 along with its device time, referred to as “receivetime3.” Device 2 now has enough information to calculate the time differential according to a similar formula.
This formula calculates the difference between the send time and the receive time for time domain messages between the two devices. If there was no variation in the time domains between the devices, then the send and receive times would reflect the communications link latency between sending and receiving the time domain messages. In one embodiment, the synchronization system assumes that the latency in transmitting a message from one device to another device is approximately the same as the latency in transmitting the message from the other device to the device. Thus, the synchronization system calculates the time domain difference by taking the average of the differences in the send and receive times of the messages. The receive time of the messages is represented by the following equations:
where Diff represents the time domain differential and L represents the latency of the communications link. These equations are equivalent to the following equations:
The average of these two equations is
The latency factors out of the equation to give the following equation:
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. The rendering devices can be components of the same physical device. For example, a DVD player may have a component that processes the video content and a separate component that processes the audio. The hardware and software of these components may result in a difference in rendering speed of the content, and thus the rendering can become out of synchronization over time. Accordingly, the invention is not limited except as by the appended claims.
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|International Classification||G06F3/14, H04N5/775, H04N5/765, G06F17/30, G06F17/00, H04J3/06|
|Cooperative Classification||G06F17/30056, H04N5/765, H04N5/775, H04L41/04|
|European Classification||H04N5/765, G06F17/30E4P1|
|Aug 8, 2003||AS||Assignment|
Owner name: BECOMM CORPORATION, WASHINGTON
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:BALASSANIAN, EDWARD;BRADLEY, SCOTT W.;REEL/FRAME:014359/0586
Effective date: 20030205
|Aug 30, 2004||AS||Assignment|
Owner name: IMPLICIT NETWORKS, INC., WASHINGTON
Free format text: AMENDMENT;ASSIGNOR:BECOMM CORPORATION;REEL/FRAME:015752/0125
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